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•58             MORPHOLOGY AND EVOLUTION
has four, of which one is the azygos lobe.   The latter is received within a snb-pericardiac pleural diverticulnm.
Urogenital Organs.—In all species there is a single papilla in each kidney, and the right kidney is posterior
to the left one.
The penis has a well-marked bone, whose characters are regarded as of taxononiic value by Pocock. The prostate gland is pyramidal with a small third lobe. The vesieulae seminales are composed of tubes and lobules, but the latter predominate in the immense vesicles in the Drill. There may be one or two ejacula-tory ducts. The testes lie in the inguinal canal, and the spermatozoa are large.
The uterus is simple, and the vagina is destitute of a hymen. Labia majora are absent, but the clitoris is large and penis-like; but it is not traversed by the urethra.
Copulation takes place in the dog-like position. During heat the female external organs and buttocks become turgid and reddened, Male animals are addicted to masturbation.
The Brain varies in complexity, but it is large. In a Common Macaque Monkey (fig. 12 D) the frontal lobes form a well-marked keel or rostrum along the inferior aspect of the great longitudinal fissure. The central sulcus (C.S.) has a slight inferior genu.
In front of the central sulcus there is a dimple representing the superior precentral sulcus (S.P.S.). The inferior precentral sulcus (I.P.S.) well merits the name "sulcus arcuatus," for it forms a bow round the inferior frontal sulcus (S.E.) or "sulcus rectus." On the inferior surface of the frontal lobe there is an H-shaped system of orbital sulci